1. Field of the Invention
The present invention relates to a rotary position sensor and more particularly to a through the hole rotary position sensor.
2. Description of the Prior Art
Devices are known for providing a signal representative of the angular position of a rotatable device. In particular, potentiometers with moveable wiper contacts were known to be used to provide an electrical signal representative of the angular position of a rotatable member. Although such potentiometers provided satisfactory results, such potentiometers were subject to wear which increased the need and frequency of replacement of such devices, thus increasing warranty costs in automobile and commercial applications.
In order to solve this problem, non-contacting sensors have been developed to provide a signal representative of the angular position of a rotatable device. Such sensors, often referred to as rotary position sensors, are known to be used in many applications including applications in the automotive industry. These rotary position sensors are non-contacting and provide an electrical signal representative of the angular position of a rotatable member, such as various automotive applications as described below.
Such rotary position sensors normally include a circular magnet rigidly attached to a rotatable device whose angular position is to be measured. A magnetic flux responsive element sensitive to magnetic flux in one plane is typically disposed and mounted stationary relative to the magnet to receive components of the magnetic flux as the magnet and rotatable device are rotated. One or more pole pieces are also typically provided. In operation, as the combination of the rotatable device and magnet are rotated, components of magnetic flux are sensed by the magnetic flux responsive element causing the output of the magnetic flux responsive element to vary as a function of the angular position of the rotatable device.
Various magnetic flux responsive elements are known to be used in such applications. Probably the most popular is a Hall effect device which provides an electrical voltage signal as a function of the magnetic flux received in a particular plane. Magnetoresistive elements (MRE), for example, permalloy, are also known. Such magnetoresistive elements (MRE) provide an electrical resistance signal proportional to the magnetic flux in a particular direction. Thus, as the magnet rotates, components of magnetic flux in one plane will vary, causing the output signal from the Hall effect device or the MRE to vary to provide a signal representative of the angular position of the rotatable device.
Two types of rotary position sensors are known; end cap and so called through the hole rotary position sensors. The particular type of rotary position used is determined by the application.
Such end cap rotary position sensors are configured to be disposed and mechanically linked to the end of a rotatable shaft whose angular position is to be sensed. Examples of such rotary position sensors used in end cap applications are disclosed in commonly owned U.S. Pat. Nos. 5,497,081 and 5,818,223, hereby incorporated by reference. In general, rotary position sensors used in end cap applications normally include a circular magnet with a central aperture, a magnetic flux responsive element and one or more pole pieces. Normally the magnetic flux responsive element is disposed adjacent the pole pieces and centrally disposed within the central aperture of the circular magnet.
As mentioned above, through the hole rotary position sensors are also known. Such through the hole rotary position sensors also include a circular magnet with a central aperture. However, in through the hole applications, the shaft of the rotatable device, whose angular position is to be sensed, is received in the central aperture of the magnet. As such, when the rotatable shaft is rotated, the magnet rotates therewith. Such through the hole rotary position sensors also include a magnetic flux responsive element and one or more pole pieces disposed adjacent the outer diameter of the circular magnet.
Various through the hole rotary position sensors are known in the art. For example, through the hole rotary position sensors are disclosed, for example, in U.S. Pat. Nos. 5,444,369; 5,742,160; 6,124,710; 6,188,216; and 6,275,025. Such through the hole sensors often include custom magnets, while other sensors require more than one magnet resulting in relatively complicated and expensive sensors. For example, the '216 patent discloses a sensor that requires two magnets, while the '710 patent requires a disc-shaped magnet. Similarly, the '025 and '369 patent also require irregular shaped magnets which can add to the cost and complexity of the sensor. Thus, there is a need for a through the hole rotary position sensor that can be formed with a relatively standard ring magnet to reduce the cost and complexity of the overall device.